1. Field of the Invention
The present invention generally relates to a linear guiding mechanism and a measuring device and, more specifically, to a linear guiding mechanism using a double parallel spring mechanism and a measuring device having the linear guiding mechanism.
2. Description of the Related Art
A double parallel spring mechanism is known as a mechanism configured to linearly guide a moving member.
For example, a mechanism configured to connect a fixed member and the moving member using two pairs (first and second) double parallel springs and to guide the moving member linearly is known (Japanese Unexamined Patent Application Publication No. 2001-281374 and Japanese Unexamined Patent Application Publication No. 2000-19415). In this configuration, a first double parallel spring mechanism and a second double parallel spring mechanism are arranged at an angle of 180° about an axis of movement of the moving member.
Also, as shown in FIG. 7, a linear guiding mechanism in which a fixed member 1 and a moving member 2 are connected by a single double parallel leaf spring mechanism 11A is also known. This double parallel leaf spring mechanism 11A includes an intermediate member 21 arranged between the fixed member 1 and the moving member 2, a pair of first leaf springs 22, and a pair of second leaf springs 23. The first leaf springs 22 connect the fixed member 1 and both ends of the intermediate member 21 and are arranged so as to be parallel to each other and orthogonal to a direction of movement of the moving member 2. The second leaf springs 23 connect an intermediate portion of the intermediate member 21 and both ends of the moving member 2 and are arranged so as to be parallel to each other and orthogonal to the direction of movement of the moving member 2.
In the linear guiding mechanism described above, in order to secure a linearity of the moving member 2, all of leaf springs 22, 23 are required to have the same restoring force. If all of the leaf springs 22, 23 do not have the same restoring force, desirable linearity is not achieved. In order to equalize the restoring force of all the leaf springs 22, 23, it is required to control the structural properties (thickness, length, etc.) of all of the leaf springs 22, 23 are the same.
Unfortunately, it is difficult to equalize the structural properties (thickness, length, etc.) of all of the leaf springs 22, 23 due to variations in accuracy of finishing. Then, as shown in FIG. 8, when the moving member 2 moves linearly, a rotary movement occurs in bending directions of the leaf springs (the directions in which the leaf springs are subjected to bend), so that desirable linearity cannot be obtained. Also, the effect of the variations in accuracy of finishing becomes remarkable as a stroke of movement of the moving member 2 is increased. As a result, the known mechanism cannot support a long stroke movement.
In the linear guiding mechanism in which the two sets of the double parallel spring mechanisms are employed, the first double parallel spring mechanism and the second double parallel spring mechanism are arranged at an angle of 180° about the axis of movement of the moving member. Thus, since the directions in which the leaf springs are subjected to bend matches between the respective double parallel spring mechanisms, the effect of compensating the variations in restoring force is small, and hence the desirable linearity cannot be obtained.